If enabled, the password will be applied only to this PC user, so the user will use this password (even if the common password is enabled) to get through the built-in screen-lock every time desktop is locked with the built-in screen-lock. If you want to use the same password for all PC users, set up the common password (see the folder "Screen Lock" in the folder "Common Restrictions" of the tree) and uncheck this option. Screen Lock is an application you can use to lock your desktop while you are away (see the icon "%LOCKNAME%" on the desktop of your PC).